Whole crudes and crude fractions with high petroleum acid content such as those containing naphthenic acids are corrosive to the equipment used to extract, transport and process the crude.
Efforts to minimize naphthenic acid corrosion have included a number of approaches for neutralizing and removing the acids from the oil. For example, U.S. Pat. No. 2,302,281 and Kalichevsky and Kobe in Petroleum Refining with Chemicals (1956), Chapter 4, disclose various base treatments of oils and crude fractions, e.g., using bases such as ammonia (page 170). U.S. Pat. No. 4,199,440 discloses treatment of a liquid hydrocarbon with a dilute aqueous alkaline solution, specifically dilute aqueous NaOH or KOH. U.S. Pat. No. 5,683,626 teaches treatments of acidic crudes with tetraaylammonium hydroxide and U.S. Pat. No. 5,643,439 uses trialkylsilanolates. PCT US96/13688, US/13689 and US/13690 (Publ. WO 97/08270, 97/08271 and 97/08275 dated Mar. 6, 1997) teach the use of Group IA and IIA oxides and hydroxides to treat whole crudes and crude fractions to decrease naphthenic acid content. U.S. Pat. No. 4,300,995 discloses the treatment of carbonous material particularly coal and its products, heavy oils, vacuum gas oil and petroleum resids having acidic functionalities with a dilute quaternary base, such as tetramethylammonium hydroxide in a liquid (alcohol or water). This patent was aimed at improving yields and physical characteristics of the products and did not address the question of acidity reduction.
U.S. Pat. No. 4,457,837 to Farnham teaches a process for treating corrosive aqueous condensate acid released from petroleum following distilation, i.e., acidic materials such as HCl and H.sub.2 S, not organic condensate. In the process the concentration of water is very high as evidenced by the requirement of a separate aqueous ammonia phase and a hydrocarbon phase. Farnham is silent on the need to form amides in the treatment process and, indeed the presence of large quantities of water disfavors such a reaction.
U.S. Pat. No. 4,634,519 to Danzik teaches a neutralization reaction of naphthenic acids upon extraction into the aqueous methanolic phase to produce ammonium salts of the naphthenic acids and requires the presence in critical ratios of alkanols, water and ammonia. Danzik indicates that about 20% water is required which is consistent with Danzik's teaching of an aqueous ammonia phase. The reference is selective and specifically states that it cannot be successfully applied to treatment of crude oils in general.
While these processes have achieved varying degrees of success there is a continuing need to develop more efficient methods for treating acidic crudes.